Effect

Generations III and IV

Block prevents the target from switching out or fleeing (including via Teleport). It bypasses accuracy checks to always hit, unless the target is in the semi-invulnerable turn of a move such as Dig or Fly. The effect only applies as long as the Pokémon that used it remains in battle.

The affected Pokémon can still switch out via Baton Pass, but in that case, the Pokémon that switches in will now be affected. Affected Pokémon can also switch out with U-turn. Conversely, the Pokémon that used Block can switch out with Baton Pass and the effects of Block will still apply. Also, if the affected Pokémon is Roared at or hit with a Whirlwind, they will still be switched out.

Generation V

If a Pokémon traps a target with Block and then switches with Baton Pass the target will no longer be trapped. Pokémon affected by Block can switch out with Volt Switch. Also, Dragon Tail and Circle Throw will force the affected Pokémon to switch out.

In the manga

In the Pokémon Adventures manga

Nosepass holds its arms out in front of it and releases a beam of energy from its body at the opponent, holding the opponent in place and preventing it from moving. The effects of the attack keeps going until Nosepass is knocked out.